Homeless John is used to describe someone who is extremely skilled, clinically insane, or someone who possesses hardcore survival skills (or all of the above). The phrase originates from Homeless John, a being that was so drunk and in so much debt that he travelled across the United States several times. He was enlisted in the Vietnam War and witnessed the killing of John alongside Daryl and Mr. Krabs. When he returned home to the USA, he was beaten for being a "war-mongering piece of shit". He claimed that he didn't know if they were Viet Cong or civilians (he knew). Later, Homeless John found himself in extreme debt to the Syrian government, so he sold his brother to them in exchange for alcohol, Cheetos, and two whole cents.
C: Hey, Dave! How was that hiking trip with Harold?
D: Harold got lost for 8 days but we met up again. He somehow found fresh water and a source of food.
C: He's such a Homeless John.
Yo, who the FUCK is this xX6AlssBeeter9Xx kid?!?! He just shot me from halfway across the fucking map! He's such a fucking Homeless John.
I'm sorry ma'am, but your son is... well, let's just say he's a Homeless John.